1. Field of the Invention
The present invention relates to the design of gyroscopic devices and, more particularly, to the design of bimetal rotor assemblies for such devices.
2. Description of the Prior Art
It is well known that the requirements for a high performance gyroscope resides principally in the angular momentum of the gyro rotor. A desired angular momentum may be obtained by selecting the speed of the rotor for a desired rotor mass or vice versa. In some applications, it may be desirable to increase the rotor mass without increasing the rotor size, and thereby reduce the rotor speed for a given angular momentum. This may be accomplished by resorting to a bimetal rotor having a high density metal rim and a low density metal bearing support web.
Bimetal gyroscopes, that is, a gyroscope having a heavy metal outer ring or rim and light metal axially spaced spin bearing support webs for mounting the rotor for spinning about an axis and thereby providing increased inertia, are known in the prior art. However, bimetal gyroscopes are not as extensively used as might be expected especially in smaller gyroscopic devices such as described in U.S. Pat. No. 3,911,591, issued to Dohogne et al, also assigned to the present assignee, due to the differential thermal expansion characteristic between the heavy weight or high density metal rim and the lightweight or low density metal web which will cause a distortion in size and/or shape of the spin bearing outer raceway thereby deteriorating the gyro performance, reliability, and life expectancy. Furthermore, a bimetal gyroscope can experience unequal axial dimensional changes and/or bearing preload changes due to centrifugal force and thermal strain effects as the gyroscope is spun up to speed and/or exposed to varying temperature causing "oilcanning" of the rim support web. For example, if the influence from the changes of the compressive stress between rim and web is axially asymmetrical, e.g., the one side of the rotor assembly relative to the other side, then the gyroscope mass will tend to shift along the spin axis to thereby unbalance the rotor/rotor bearing frame assembly and cause unacceptable gyroscopic drift. Panel mounted aircraft instrumentation gyroscopes, such as shown in the above Dohogne et al patent, moreover, are spaced limited which generally prevents incorporation of radial expansion schemes.
Accordingly, there may be many applications for bimetal gyroscope rotors with means which eliminates spin bearing outer raceway distortion and axial dimensional changes due to thermal and centrifugal effects.